Plasma systems and methods including high enthalpy and high stability plasmas

ABSTRACT

The present disclosure generally relates to systems, apparatus and methods of plasma spraying and plasma treatment of materials based on high specific energy molecular plasma gases that may be used to generate a selected plasma. The present disclosure is also relates to the design of plasma torches and plasma systems to optimize such methods.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/771,908, filed Feb. 20, 2013, now U.S. Pat. No. 9,150,949, issuedOct. 6, 2015, which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/608,426, filed on Mar. 8, 2012, which is fullyincorporated herein by reference.

FIELD

The present disclosure generally relates to systems, apparatus andmethods of plasma spraying and plasma treatment of materials based onhigh specific energy molecular plasma gases that may be used to generatea selected plasma. The present disclosure is also related to the designof plasma torches and plasma systems to optimize such methods.

BACKGROUND

One major goal of plasma spraying and plasma treatment of materials maybe generating of stable plasmas having a capability to control within arelatively wide range the heat and momentum transfer to feedstock, thusproviding desirable parameters (temperature, velocity, etc.) offeedstock to form a deposition with required properties. Additionalgoals my include control of substrate temperature as well as otherconditions of a deposit formation.

Heat transfer from plasma to feedstock may be characterized by HeatTransfer Potential (HTP) which is the major parameter determining plasmaability to heat particles and substrate:HTP(T)=∫_(T) ₀ ^(T)λ(T)dTwhere λ is plasma thermal conductivity; T is plasma temperature. HTP mayhave a correlation with plasma specific power (SP), plasma enthalpy Hand plasma temperature. Plasma specific power SP, related plasmaenthalpy H and thermal efficiency η may be determined as follows:SP=U*I/Gp; H=SP*η; η=1−Lw/(U*I)where Lw is power losses into cooling media (water); U is plasma torchvoltage; I is plasma current; and Gp is plasma gas total flow rate.Specific power SP may be directly measured to characterize plasmaconditions and further calculations of plasma HTP, H and temperature.So, SP will be used below for plasma characterization. It may be notedthat sometimes power source or control system voltage readings are usedas the torch voltage for the calculations. In this case calculated SPand H may be slightly above the real values due to a voltage drop inpower cables connecting a power source with a torch.

FIGS. 1 and 2 illustrate the correlations between plasma HTP, H andtemperature for argon and N₂ based plasmas with input data taken fromthe literature, such as Thermal Plasmas: Fundamentals and Applications,Volume 1, Boulos, Facuhais, Pfender, Plunum Press, New York (1994)(“Thermal Plasmas”). Generally, increase of plasma specific power andrelated enthalpy results in increasing of plasma temperature and HTP.However, for N₂ based plasmas, plasma temperature corresponding to aparticular HTP and related enthalpy may be significantly lower thanplasma temperatures corresponding to argon-based plasmas under the sameconditions. This is due to the energy needed for the moleculedissociation. For instance, at HTP≈8000 W/m argon based plasmas may havetemperatures exceeding 9000° K while nitrogen based plasmas temperaturemay be below 7000° K (see FIGS. 1 and 2). CO₂ and Air plasmas may haveeven slightly higher HTP in comparison with N₂ plasma at the same plasmatemperature.

For the major part of plasma treatment of materials feedstock injectioninto a plasma jet generally takes place downstream of anode arc rootattachment and, very often, even downstream of the plasma torch nozzleexit. It may be noted that HTP may decrease significantly downstream ofthe anode arc root attachment plasma jet due to plasma radiation as wellas plasma mixing/interaction with ambient air downstream of the nozzleexit. Decreasing of HTP may result in decreasing of feedstock activedwell time t_(d) when HTP value is sufficient for effective heattransfer from plasma to the feedstock. Intensity of plasma interactionwith ambient air may be controlled by plasma velocity including velocitydistribution as well as by radial and tangential components of plasmavelocity. Plasma radiation heat losses Qr mainly depend on plasmatemperature and may be estimated using a formula:Qr˜ε(T,P)σ_(SB) T ⁴where σ_(SB) is Stefan-Boltzmann's constant; ε(T,P) is “degree ofgreyness” and ε=1 corresponds to the “absolute blackbody” radiation. Itmay be noted that for the typical plasma-spray parameters c is much lessthan 1 and rapidly grows with the temperature and pressure. Thus, theactual temperature dependence of the radiation flux could besignificantly stronger than T⁴.

Estimates may show that plasma jet radiates so intensively above plasmatemperature T≈9000-10000° C. that all additional energy heating plasmaabove this temperature may be lost within 2-3 cm downstream to nozzleexit and plasma temperature may become there below T≈9000-10000° C. withrelated decreasing of HTP and enthalpy. Thus, based on FIGS. 1 and 2 aswell as on Table 1 below it may be concluded that the HTP of Ar basedplasmas having up to 20 vol. % H₂ may not exceed HTP≈7-10 kW/m atdistances above 2-3 cm downstream of a nozzle exit. For Ar-50% H₂ HTPmay achieve 14-16 kW/m. However, plasmas with more than 25-30 vol. % ofhydrogen with Argon may have a significant pulsing of plasma parametersthat their practical application may be very limited.

N₂ based plasmas may provide significantly higher HTP at the sametemperatures utilized for Argon. For example, N₂—H₂ plasma having 20vol. % of H₂ may provide HTP up to 18 kW/m before plasma temperaturesmay achieve T≈9000-10000° C. and the radiation may dominate in theenergy balance thus resulting in extremely fast decrease of HTP. Thesame may be stated regarding plasmas based on other molecular gases likeAir and CO₂.

TABLE 1 Plasma HTP and Enthalpy corresponding to 9,000-10,000 K plasmatemperature for argon and nitrogen based plasmas Plasma gas (vol. %) ArAr + 20 H₂ Ar + 50 H₂ N₂ N₂ + 20 H₂ N₂ + 50 H₂ HTP, kW/m 2-3 7-10  14-1612.8-14.8 15.9-18.3 17.5-20.5 H, kJ/g 5-6 10-11.5 24-27 48-53 54.8-60    58-64.5

In addition, it has been observed that in the case of Ar—H₂ and N₂—H₂plasma jets, it may be seen that length of high temperature/high HTPcore part of Ar—H₂ plasma jet is significantly shorter than N₂—H₂ onedue to intensive radiation. It may result in significantly shorterfeedstock active dwell time t_(d) and related lack of heat transfer tothe feedstock. Thus, it may be concluded that only molecular gases basedplasmas may be beneficial when high SP, H and HTP as well as long activedwell time are needed to achieve desirable properties of a deposit.However, it may be noted that molecular gases based plasmas may causeexcessive wear of electrodes, plasma instability, pulsing and drifting.With respect to plasma systems, different approaches may be used toavoid or minimize these disadvantages. For example, different plasmapassage configurations have been used to stabilize anode arc root axialposition of the plasma apparatus thus minimizing voltage pulsation dueto the arc shunting. Reference is made to U.S. Pat. Nos. 4,841,114 and6,114,649. It may be noted that presently the PLAZJET® systemmanufactured by Praxair-TAFA and having maximum power of about 200 kWmay generate stable high SP molecular gases based plasmas simultaneouslyproviding long life of electrodes. For N2-H₂ plasmas maximum reported SPlevel may be of about 42.5 kJ/g.

SUMMARY

A method and apparatus for depositing a coating from a plasma torchcomprising supplying a plasma torch generating voltage (U) above 100 Vand current (I) below 500 A comprising a cathode electrode, an anodemodule having an anode electrode having an anode axis, entrance zone anda cylindrical zone having diameter Da wherein said plasma torchgenerates a plasma arc having an anode arc root attachment inside saidanode. A plasma jet forming module is located downstream of the anodearc root attachment which forming module controls one or more parametersof the plasma jet in said module. An interelectrode module controllingthe plasma arc passage between said cathode and said anode is suppliedhaving one end adjacent the cathode module and a second end adjacent theanode module and having a pilot insert adjacent to said cathode. Thereis at least one neutral inter-electrode insert and the plasma torchfurther comprises two passageways to feed plasma gas in a total amount Gwherein the plasma gas comprises more than 50 vol. % of molecular gas.One may then supply a feedstock into the plasma jet and deposit acoating on a substrate wherein one of the passageways for feeding plasmagas comprises a first plasma gas passage located between the cathode andpilot insert for feeding plasma gas in amount G1 wherein the gas isdirected through a plurality of orifices having a surface area S1wherein a vortex is formed having a vortex intensity Vort1=G1/S1. Inaddition, one of said passageways for feeding plasma gas comprises asecond plasma gas passage located between said interelectrode module andsaid cylindrical part of anode for feeding plasma gas in an amount G2wherein the gas is directed through a plurality of orifices having asurface area S2 wherein a vortex is formed having a vortex intensityVort2=G2/S2. The value of G1 is greater than 0.6G and Vort1=G1/S1 isgreater than 0.1 g/((sec)(mm²)) and wherein (U)(I)/(G) is in the rangeof 43 kJ/g-140 kJ/g.

BRIEF DESCRIPTION OF THE FIGURES

Features and advantages of the claimed subject matter will be apparentfrom the following description of embodiments consistent therewith,which description should be considered in conjunction with theaccompanying drawings, wherein:

FIG. 1 illustrates a HTP correlation with plasma enthalpy (H) fordifferent gases.

FIG. 2 illustrates a HTP dependence on plasma temperature.

FIG. 3 illustration a schematic of a cascade plasma system.

FIG. 4 illustrates a torch having expended plasma passage inside IEImodule.

FIG. 5 illustrates one of possible embodiments of a transition zone (G2feeding into upstream area of anode entrance zone).

FIG. 6 illustrates one of possible embodiments of a transition zone(Conical portion of the anode entrance zone and G2 feeding into a slot).

FIG. 7 illustrates a plasma jet forming module.

FIG. 8 illustrates a plasma jet “angled” forming means.

FIGS. 9 a-b illustrate axial feeding of additional gases into thestepped expansion of the plasma jet passage.

FIGS. 10 a-b illustrate radial feeding of additional gases into thestepped expansion of the plasma jet passage.

FIGS. 11 a-c schematically illustrate various aspects of an embodimentof a plasma jet control system consistent with the present disclosure.

FIG. 12 illustrates a possible embodiment of an apparatus.

FIGS. 13 a-b illustrate cathode vortex distributor.

FIGS. 14 a-b illustrate an embodiment of the downstream neutral insert84 having 6 vortex holes.

FIG. 15 contents information related to Examples 1-7

DETAILED DESCRIPTION

The present disclosure, as noted, relates to systems and methods ofplasma spraying and plasma treatment of materials based on high specificenergy plasma gases. Specific power molecular gas based plasmas withSP>43 kJ/g may now be achieved which may also improve heat transfer tofeedstock and, consequently, improve deposit quality and overall processefficiency. Preferably, the specific power molecular gas based plasmasherein may include those with SP up to 120-140 kJ/g. Levels higher than140 kJ/g even for nitrogen—hydrogen plasmas may result in plasmatemperatures above 9,000-10,000K and all additional SP may be radiated.

Current above 500 A may cause excessive erosion of an anode whenmolecular gases are used. Thus, the present disclosure allows for theuse of relatively high voltage above 100V and relatively low currentbelow 500 A. This in turn may provide advantages in the generation ofrelatively high specific energy (>43 KJ/g) and related HTP plasmas. N₂,air and CO₂ based plasmas are the preferred molecular gases herein.However, N₂ based plasmas may be most preferred as they may not generatefree oxygen in the plasma jet and result in some undesirable outcomeslike relatively intensive oxidation of metallic alloys during spraying.

FIG. 3 illustrates a schematic illustrate of plasma system formodification and optimization herein. As shown the plasma system 2 maygenerally be based on a plasma torch 4. The plasma system 2 may includea variety of modules. The plasma system 2 schematically depicted in FIG.3 may include a DC power source module (PS); control module (CT), whichmay control plasma gases flow rates, the plasma current and voltage,sequence of events during plasma start up and shut down, etc.; plasmaignition module (IG) and ignition circuit 16. The plasma torch 4,itself, may include a cathode module C having at least one cathode 122;an inter-electrode inserts module (IEI) expanding and stabilizing thearc; and an anode module (A). Inter-electrode inserts module may includea Pilot Insert (PI), and at least one neutral inter-electrode insert(NI). A plasma jet forming module (F) may be located downstream of anodearc root attachment for shaping and/or controlling the velocity andtemperature of a plasma jet (PJ) exiting the torch. The forming meansmay be arranged as a separate module electrically insulated from anodemodule (A) in this case. The plasma jet forming means (F) may be alsoangled, which may provide the possibility of spraying on internalsurface of parts and inside other confined spaces. A Feedstock Feedingmodule (FF) may be provided for introducing a material feedstock into aplasma jet (PJ) of plasma generated by the plasma torch 4. The FeedstockFeeding module may be located downstream of anode arc root attachmentand may feed feedstock into a forming means (position 6) or into aplasma jet (position 8). Material feedstock may be in a form of powder.It may also be in a form of liquid precursor or suspension of finepowders in liquids like ethanol or water. Solid feedstock like wire,rod, and flexible cord may be used as well.

A plasma gas G1 may be supplied to the cathode area, e.g., a spaceformed between the cathode 122 and pilot insert PI, through a passageinside the cathode module C. The plasma gas G1 may be the only gas usedto generate plasma. Gp=G1 in this case.

A second plasma gas G2 may also be used to generate the plasma. Thesecond plasma gas G2 may be supplied through a passage located betweenIEI module and Anode module as shown on FIG. 3. Still further additionalplasma gasses may also be used to form the plasma. Such additionalplasma gases may be supplied through passages formed in and/or betweeninter-electrode inserts. According to other embodiments, for example, athird plasma gas G3 may also be used to generate plasma. The thirdplasma gas G3 may be supplied through a passage between the pilot insertPI and the adjacent inter-electrode insert of the inter-electrodeinserts module IEI. Gp=G1+G2+G3 in this case. G1, G2 and the additionalgases may also reduce erosion of electrodes and inserts, undesirablepossible arcing between various modules, pilot and neutral insertsand/or minimize erosion of electrodes, control plasma composition, etc.It may be noted that implementation of G3 and other possible additionalplasma gases may result in the minor advantages dealing with the torchperformance, however resulting in the torch design complexity andrelated maintenance and service challenges.

The cathode 122 may be connected to a negative terminal of a DC powersource PS. In one embodiment, the DC power source may produce low ripplecurrent, which may increase the stability of plasma parameters. A verylow ripple may be achieved, for example, by using a ripple cancellationtechnique. An example may be DC power sources ESP-600C or EPP-601manufactured by ESAB. During plasma ignition the positive terminal ofthe power source may be connected to the pilot insert PI through theignition circuit 16.

According to an embodiment here, the ignition circuit 16 may include theignition module IG, resistor 18, switch 14, control elements,capacitors, choke, and inductors (not shown). The ignition module IG mayhave a high voltage, high frequency oscillator. The oscillator mayinitiate a pilot electrical arc 10 between the cathode 122 and the pilotinsert PI. The DC power source PS may be employed to support the pilotarc 10. The pilot arc 10 may ionize at least a portion of the gases in apassage 26 formed by sub-passages which may have different diameter forpassage of plasma. That is, pilot insert PI may be of one diameter,neutral inserts (NI) may have other diameters, and the anode may definea particular diameter for plasma passage. The low resistance path formedby ionized gas may allow initiation of a main arc 12 in an arc passage26 between cathode 122 and anode module A. The switch 14 may bedisengaged after the main arc 12 has been established, thus interruptingthe pilot arc 10. Consistent with one embodiment, several switches (notshown) may be connected to inter-electrode inserts to generate arcsbetween the cathode 122 and the inter-electrode inserts connected to theswitches. Similar to the pilot arc 10, the arcs between the cathode 122and the inter-electrode inserts may provide a low resistance path tofacilitate initiation of the main arc 12, in the event that the lengthof the main arc 12 is greater than the capability of the ignitioncircuit utilizing only pilot insert PI.

Plasma arc passage 26 may have different arrangements and options.Plasma passage inside PI may have diameter Dp and length Lp. FIG. 4shows diameters Dp, D₁, D₂, D₃, D₄, D₅ up to DN. Plasma passages insidea neutral insert number “i” may therefore be designated to diameter D(i)and length Li. In some embodiments Dp may be the same or smaller thandiameter D(1) of the adjacent (downstream) insert. Diameters of allneutral inserts (NI) may be the same as depicted on FIG. 3. Diameters ofneutral inserts may also increase downstream providing D(i+1)≧D(i) asillustrated on FIG. 4.

The present disclosure now controls plasma passage diameter and profilesat the same plasma gases flow rates, SP and enthalpy which may now be aparticularly effective tool to control plasma velocity separately ofplasma temperature. For example, expanding diameter of plasma passageproviding larger diameter of an anode may result in relatively lowerplasma velocity in comparison with a cylindrical plasma passage having arelatively smaller anode diameter. Plasma velocity and related feedstockdwell time control may be very beneficial when different size ofparticles of the same material are needed to achieve differentproperties if deposits. One example is a porous thermal barrier coatings(TBC) sprayed by different size of yttria stabilized zirconia powders toachieve different porosity and pores size.

The plasma torch 4 may be capable of using a relatively high-voltage,relatively low current approach, which may suitably be used with a widerange of plasma gas flow rates, related SP, HTP and plasma velocity.Such a plasma torch may also be capable of realizing laminar,transition, and turbulent plasma jet flows. Generally, the plasma torch4 may operate in a wide range of plasma current (e.g. 150 amps-500amps). The length of arc (La) and related voltage values and theirvariations may depend on stability of arc in the area adjacent tocathode and inside IEI module, total length of IEI module as well asposition of anode arc root attachment (15) inside anode. See FIG. 3.Length of the IEI module may depend on the amount of neutral inserts(NI) and their thickness (5.0 mm-25.0 mm). Position of anode arc rootattachment may have axial instability and fluctuations due to arcshunting, which may result in undesirable voltage fluctuations andrelated instability of plasma jet parameters.

The present disclosure is therefore, now capable of generating plasmaswith SP>43 kJ/g using gases having more than 50 vol. % of moleculargases. Such may then provide:

-   -   Specific Power (SP) and related parameters stability with long        term variations (drifting) below 1% of the setup values    -   Minimum pulsing of plasma voltage on a level below 5-10 volts    -   Capability to control plasma jet velocity and temperature,        effective, homogeneous treatment of feedstock, high deposit        efficiency and deposit quality

Several variables may be now considered and optimized to achieve one ormore of these features. These variables are:

1. Plasma Current

The initial consideration is plasma current. In the context of thepresent disclosure, plasma current may be preferably at or below 500 A,and in the range of 150 A to 500 A. Such current levels may providerelatively long life of the electrodes. The most preferable range ofcurrent is 200-400 A. At current above 500 A even high efficiency gasswirls may not provide sufficient rotation of anode arc root needed tocontrol the heat flux especially to anode. Thus, additional, forexample, electro-magnetic means to rotate the arc may be needed toprovide long life of a torch at current above 500 A.

As current may be controlled to preferably less than 500 A, voltage Umay now be preferably controlled and adjusted in accordance with theneeds regarding plasma specific power SP=U*I/Gp for a particular plasmagas and flow rate. Again, SP is preferably >43 kJ/g. Voltage control maybe done most preferably by controlling the arc length which depends onthe total length of the IEI module. Additional less preferred voltagecontrol may be also used. For example, relatively smaller diameter ofplasma passages formed by a pilot insert and/or neutral inserts mayresult in relatively higher voltage.

2. Cathode Gas (G1) Having Tangential Component (Vortex)

The stability of the arc in the area adjacent to cathode and inside IEImodule may be achieved by providing G1 having a tangential component ofvelocity, thus creating vortex in the area located between the cathodeand pilot insert. The vortex may propagate downstream along plasma arcarea thus may cause stabilizing of the arc additionally to wallstabilization by IEI.

In the present disclosure, the G1 flow rate may now be more than 60 vol% of total plasma gas flow rate, which means G1>0.6 Gp, to preferablysupport the vortex propagation along the plasma channel inside the IEImodule. See again, FIG. 3. The vortex intensity may be characterized bya ratio Vort1=G1/S1 where S1 is a surface area of the G1 vortexorifices.

At relatively small G1 flow rates corresponding to SP>43 kJ/g usefulstabilization of the arc may be observed for the vortex generated by G1,namely when Vort1>0.1 g/(sec*mm²). Plasma gas flow is measured in g/secand surface area is measured in mm² to calculate the vortex intensity.Other units of measurements may be used as well with related changes inthe calculated values of vortex intensity. Generally, higher intensityof the vortex velocity may result in better stabilization of the arc andthe intensity of the vortex may be limited by sonic velocity of plasmagases. Higher velocity of the vortex may also result in higher availableplasma velocity control rate (Δ), which is described more fully below.

3. Anode Plasma Gas (G2) Having Tangential Component (Vortex) to RotateAnode Arc Root Attachment

Use of only G1 at certain flow rates may not be sufficient for the anodearc root attachment rotation and stabilization when relatively lowplasma gas flow rates are needed to generate high SP plasmas (>43 kJ/g).It may be explained by downstream decrease of the vortex intensity dueto viscous plasma flow inside the plasma channel. Decreasing of vortexintensity may also limit available plasma velocity control rate.Insufficient vortex in the area of anode arc root attachment may resultin both unstable arc root rotation and related short life of anode aswell as excessive axial fluctuation of arc root position resulting inexcessive pulsing of plasma jet.

The above disadvantage (unstable root rotation) may now be minimized orcompletely avoided by providing G2 with a tangential component of thegas velocity providing the same rotation direction as G1, which occursbefore the anode arc root attachment. Positive effect of G2 addition toG1 may be observed from some minimum value G2,min. The minimum flow rateG2,min which may be needed for efficient anode arc root rotation maydepend on anode diameter Da and may be defined as G2,min=(0.01-0.025)Dawhere Da is measured in mm and G2 is measured in g/sec.

Minimum vortex intensity related to G2 may be on the same level as forG1, i.e. Vort2>0.1 g/(sec*mm2) However, G2 flow may be lower than 0.4 Gpin this case which may follow from G1>0.6 Gp. The techniques to feed G2into the plasma channel may be preferably located relatively close tothe anode arc root attachment, preferably 3-25 mm upstream of the arcroot attachment. Thus, by feeding G2 close to the anode arc rootattachment, a minimum or no decrease of vortex intensity in the area ofarc root attachment may be expected which may result in relatively longlife of an anode.

G2 maximum vortex intensity may be estimated as Vort2(max)=0.4g/(sec*mm2). Increasing of Vort2 above this level may not be desirableand may result in excessive tangential component of plasma jet velocityand related disadvantages dealing with material feedstock precisefeeding into the desirable areas of plasma jet. Thus, the vortex rangeof intensity may be disclosed as 0.4 g/(sec*mm2)>Vort2>0.1 g/(sec*mm2).Combination of G1 and G2 vortices with the disclosed flow rates andintensity may already result in relatively high stability of plasmashaving SP>43 kJ/g

4. Methods to Stabilize Anode Arc Root Position

It is preferred to now arrange the transition zone 24 in the plasmapassage between IEI module and cylindrical part of an anode withsimultaneous positioning of G2 vortex feeding methods inside thetransition zone. This may result in further decrease of the arcinstability and pulsing within wide range of operating parametersincluding parameters providing specific power SP>43 kJ/g.

FIG. 5 illustrates one of the preferred embodiments of the transitionzone 24 which may include an expansion 30 downstream of the end ofplasma passage 26 inside of the IEI module. The expansion 30 maytherefore be configured such that a discontinuity occurs in the passage26 thereby causing a distortion in the plasma flow. Preferably, the flowof plasma is distorted due to the feature that the zone 24 includes anexpansion surface 24 a to provide a diameter increase in the plasmapassage.

A ceramic ring insulator 28 is positioned in a slot 24 b between the IEImodule and the anode module A. The anode has an entrance zone 24 c andcylindrical portion 44 and diameter Da associated with cylindricalportion 44. Preferably there are minimum or no losses of G2 vortexintensity in transition zone 24. Slot 24 b may be approximately 1.5-3 mmwide and may as noted contain the ceramic ring 28 insulating the IEImodule from the anode module.

Length Le of the anode entrance zone 24 c may be of the same order as Daand Le and may be preferably defined as Le=(0.5-1.5)Da. G2 swirl plasmagas may be fed in zone 24 b (G2-b) and/or in zone 24 c (G2-c) which isillustrated in FIGS. 5-6. The anode entrance zone may have differentgeometric shapes. For example, FIG. 6 illustrates a conical portion 46of entrance zone 24 c while FIG. 5 illustrates a rounded entrance zone24 c. It should be noted that G2 orifices may locate on diameter D(G2)illustrated in FIGS. 5-6 which preferably are at least 2-3 mm largerthan anode diameter Da.

Analysis of ID anode surfaces may reveal that the anode arc rootattachment locates preferably near or on the upstream portion of thecylindrical portion 44 of the anode. The maximum observed downstreamposition of anode arc root attachment may be preferably characterized byLc which is illustrated in FIG. 5. As a rule, Lc<(1-1.5) Da. Thus, totalanode length La=Le+Lc may be estimated as La=(1.5-3)Da and the arealocated downstream of the maximum value of La serves as the plasma jetforming portion F.

It was surprisingly observed that introduction of the transition zonetogether with the disclosed above specifics of swirls G1 and G2 mayresult in the capability to control significantly plasma passagediameter and profiles within a relatively wide range at the same plasmagases flow rates and plasma thermal conditions including plasma SP, HTP,enthalpy and temperature. It may be an effective tool to control plasmavelocity without significant variations of plasma thermal conditions.FIG. 4 illustrates one of possible plasma passage profiles which may beused to realize independent plasma velocity control. In this embodimentDp>D1>D2>D3>D4>D5. Symbol DN may be also used for the diameter of thelast downstream insert of IEI module which is adjacent to an anode(insert #5 on FIG. 4).

Rate of the available velocity control (Δ) may be determined as a ratiobetween maximum plasma velocity Vmax and minimum plasma velocity Vminachievable by a plasma spraying method at particular thermal conditionsof plasma. Thus, Δ=Vmax/Vmin. Higher available Δ may result in improvedcapability of the plasma spraying method herein, along with wideroperating windows and related practical benefits. The velocity of plasmaexiting an anode may be approximately proportional to 1/(anode surfacearea), i.e. V˜1/Da². Thus, Δ may be estimated as Δ=(Da,max/Da,min)²where D(a, max) and D(a, min) are maximum and minimum diameters of thecylindrical part of anode which may be achieved by preferablycontrolling the plasma passage profile and diameter with no orrelatively minor changes in the plasma thermal conditions. The followingdata regarding the rate of velocity control (Δ) and related parameterswere obtained based on a plasma torch used for the methods herein.

-   -   Available variation of Da still providing relatively stable arc        may be estimated on a level of Da=(0.8-1.25)DN which gives        Δ=(1.25/0.8)²≈2.4. Higher rate between Da and DN in this case        may cause plasma instability. Thus, additional profiling of        plasma passage may be needed when higher rates of plasma        velocity control is needed    -   Additional profiling of the plasma channel may allow achieving        Δ≈3.65 for Da,min of about 6 mm and Da,max of about 11.5 mm. It        may be also noted that Da,max=11.5 mm was limited by a        particular design of the torch where dimensions of the anode        housing may not yield an anode with Da>11.5 mm. So, it is        contemplated that higher values of Δ may be achieved if needed        by scaling up the design of the anode housing and related        dimensions of the anode.

5. Means to Minimize Tangential Component and Equalize PlasmaTemperature and Velocity Profiles

Effective plasma arc stabilization and anode arc root rotation by swirlsG1 and G2 disclosed above may result in the high relative intensityswirling flow of the plasma jet downstream of the anode arc rootattachment. In this case a relatively excessive tangential component ofthe velocity of the plasma jet may consequently result in excessivemixing of plasma jet with ambient air, related shortening of high HTPcore part of plasma jet and decreasing of active feedstock dwell time tdas well as resulting decreasing of efficiency of feedstock treatment inthe plasma jet. Thus, it may be very desirable for various applicationsto have a plasma jet forming portion located downstream of the anode arcroot attachment which may minimize the tangential component of plasmajet velocity.

The minimized tangential component may then result in relativelyminimized mixing (interaction) of the plasma jet with surrounding media(air) and, consequently, relatively longer high temperature maintenanceof the jet and relatively longer active dwell time. A relativelyminimized tangential component may also result in better controllablefeedstock injection into desirable areas of plasma jet and, thus, betterdeposit quality and deposit efficiency. Different additionalrequirements to plasma jet parameters may also request additionaldifferent configurations of a forming nozzle.

Abrupt stepped expansion of the plasma jet passage diameter from Da toDs with a following cylindrical plasma jet passage having diameterD_(S)>Da may be an efficient way of decreasing the plasma tangentialcomponent. This expansion may be characterized by step angle β,expansion ratio δ, and expansion angle α which is illustrated by FIG. 7.Step angle β may be of about 90° with acceptable variations of about+/−10°. Generally, it may be expected that higher jet expansion angle αand larger expansion rate may result in lower tangential component ofvelocity of plasma jet exiting the forming nozzle. However, surprisinglyit was found that jet expansion angle α>25° may also result in theshortening of plasma jet which may be explained by a significant amountof ambient air which may penetrate inside the over expanded nozzle andhave a negative influence on the jet formation. Additionally, it wasfound that decreasing of the expansion angle α<8° may not result insufficient decreasing of the plasma velocity tangential component.However, it may result in the increasing of the nozzle length and,therefore, it may result in additional heat losses due to the heatexchange between the nozzle wall and plasma. Thus it may be concludedthat a positive effect of the swirl decreasing may be expected withinthe preferred range 8°>α>25°. The most pronounced effect may be observedwithin α≈10-18°.

Optimum expansion ratio δ may be understood as 0.2 Da<δ<0.6 Da. At δ<0.2Da decreasing of the tangential component may be relativelyinsignificant or even may not be observed. At δ<0.6 Da furtherdecreasing of the tangential component was not observed. However,further increasing of the related nozzle length may result in theincreasing of heat losses already described above. It may be noted thatsuch a stepped expansion of the plasma passage may also result inequalizing of plasma jet temperature and velocity across the jet profilewhich may result in further improvement of homogeneity of treatment offeedstock powders or suspension, etc, high deposit efficiency anddeposit quality.

The stepped expansion of the plasma jet passage may be located underangle γ to the anode axis which illustrated by FIG. 8. Angle γ may varywithin 0-90° based on a technology requirements. Generally, γ maypreferably be within 45°-80°. A variety of feedstock feeding options maybe utilized by the method which is illustrated on FIGS. 7 and 8(positions 6 a-6 c, 8). It may be also noted that the stepped expansionof plasma jet passage downstream of an anode arc root attachment may beused for other plasma spray processes/torches and not the plasma jetconfigurations specifically described herein. In this case the expansionmay be arranged at a distance of about (1-2)Da downstream of arc rootpreferable attachment area.

Feeding of additional gases into the stepped expansion may also assistformation of a desirable plasma jet parameters and further decrease thetangential component of plasma velocity. FIG. 9 illustrates an optionwhen additional gases may be fed through multiple gas passages 32located axially to plasma jet. FIG. 10 illustrates radial gas passages34 for feeding of additional gases and providing them with a swirl whichmay have a direction contrary to the plasma jet swirl generated by G1and G2.

6: Deflection Jet

A plasma apparatus consistent with the present disclosure may generate aplasma jet having a high specific power and temperature. In some cases,high plasma temperature and specific power may result in undesirableoverheating a substrate being spray coated with the plasma apparatus.For example, it may happen when short spray distance must be used forspraying due to a confined space. Overheating of the substrate mayproduce stress in the coating and/or defects related to agglomeration offine particles, e.g., having a size below about 5-10 micrometers, aswell as various other defects. Generally, such defects may be describedas “lamps” or “bumps”. It may be also noted that in a case of metallicalloy coatings spraying high plasma enthalpy and temperature may alsoresult in undesirable over-oxidation of the fine particles and resultantexcessive amount of oxides in a coating. According to one aspect,overheating a substrate, and the resultant increase in defects, as wellas oxides content in metallic coatings may be minimized by employing adeflection gas jet in the region of the coating application.

Referring to FIGS. 11 a-c, a compressed gas deflection jet may beapplied across the plasma jet 210 containing feedstock by a deflectiongas nozzle 214 a. The gas nozzle 214 a may be disposed outside of thespray pattern generated by the plasma apparatus 4 and may be directedgenerally parallel to the substrate 212 a, and/or at a slight anglethereto, in the region of the spray pattern or above it. According toone embodiment, the nozzle 214 a may be positioned just outside of thespray pattern, while in other embodiments the nozzle 214 a may belocated further away from the spray pattern. Different configurationsfor locating the nozzle 214 a and 214 c are illustrated in FIGS. 11a,and 11c . The deflection gas nozzle 214 may have a generally rectangularprofile, as depicted in FIG. 11b . The nozzle 214 may be wider than thespray pattern produced by the plasma apparatus 4. For example, thenozzle 214 may have a width in the range of about 30-50 mm for a spraypattern in the order of 25 mm wide. In one embodiment, the height h ofthe nozzle 214 b may be in the range of about 1-4 mm. The compressed gasof the deflection jet may be air, nitrogen, etc., and may be supplied ata pressure on the general order of around 3-6 bars. The deflection gasjet may deflect the plasma jet 210 generated by the plasma apparatus 4,along with any fine particles, for example particle having a size lessthan about 5-10 microns. Larger particle may have sufficient mass, andtherefore inertia, to pass through the deflection jet without beingsubstantially deflected.

The above description of the plasma spraying system may now be providedin a more detailed apparatus form that is entirely consistent with thedisclosure and description above in FIGS. 3-11.

Attention is therefore now directed to FIG. 12. Cathode Module C mayhave a cathode base 124 with cathode insert 122, cathode housing 128,cathode holder 144, cathode nut 132, and cathode vortex distributor 126.Cathode base 124 may be made of high conductivity material, e.g. copperor copper alloy. Cathode base 124, cathode 122 and cathode nut 132 mayhave electrical contact with cathode holder 144. Cathode holder 144 maybe connected to a negative terminal of a DC power source shown on FIG.3. Pilot insert 80 may have an electrical contact 86 with cathodehousing 128 which during ignition may be connected to a positiveterminal of a DC through a resistor 18 and switch 14 shown on FIG. 3.Cathode housing 128 and cathode holder 144 may be electrically insulatedfrom each other by cathode insulator 152

Cathode housing may have a gas passage 130 to feed G1 portion of aplasma gas. The gas passage 130 may be connected with cathode vortexdistributor 126 having a circular gas receiver 134 connected with radialmultiple gas passages 146 which, in turn, are connected to correspondingaxial passages 136. Each axial passage 136 may be connected with thevortex holes 138. Sealing O-rings 148 may be used to seal the gaspassages.

FIGS. 13 a-b illustrate additional features of an embodiment of cathodevortex distributor 126 having 6 holes. The amount of holes (more than 3at a minimum) and their diameters may be used to control the vortexintensity Vort1 and to adjust it satisfying requirements disclosedabove. For example, using six holes as a representative case, thediameter of the vortex Dvor1=0.8 mm and surface area S1 is approximately3 mm². Thus, this vortex distributor may be used for G1>0.3 g/sec. TheG1 top limit depends on a sonic velocity as was mentioned above and maybe estimated for each particular plasma gas. For example, at roomtemperature sonic velocity and density for nitrogen are about 334 m/secand 1.165 kg/m3. Thus, in accordance with the disclosure range ofnitrogen flow rate through surface area 3 mm² may be estimated atapproximately 15-60 L/min. For other ranges of vortex gas flow amountand/or diameter of vortex holes in the cathode, the vortex distributor126 may be adjusted accordingly.

An inter-electrode inserts module may consist of a pilot insert 80 andone or more neutral inserts. Four neutral inserts 81-84 may be used inthe depicted embodiment. Inserts 81-84 may have the same diameter asshown on FIG. 12. Diameters of neutral inserts may also increasedownstream as shown on FIG. 4 providing plasma passage profile andrelated independent plasma velocity control. The neutral inserts may beelectrically insulated from each other and from pilot insert 80 by a setof ceramic rings 88 and sealing O-rings 90.

Generally, the amount of inserts may be changed providing differentplasma voltage ranges and satisfying other possible requirements. Forexample, only inserts 81 and 84 may be used in the embodiment if thetorch length needs to be shortened. For N₂ plasma having G1=0.58g/sec≈30 L/min, G2=0.29 g/sec≈15 L/min≈ and operating at 400 A removalof the middle inserts 82 and 83 results in decreasing of plasma arcpassage inside IEI module from about 52.5 mm to about 32.5 mm, relatedoperating voltage decreasing from 201V to 162.5V with the decreasing ofthe Specific Power (SP) from approximately 92 kJ/g to 74 kJ/g. Arequirement to increase SP may be satisfied, for example, by use of 6neutral inserts with related increasing of operating voltage up to about240V and specific power up to about 110 kJ/g at the same current and N₂flow rates.

Anode module A may consist of anode housing 48 and anode 50. The anodemay have an entrance converging zone 24 c connecting with a cylindricalzone 44 having diameter Da. Transition zone 24 in the plasma passagebetween IEI module and cylindrical part 44 of the anode in thisembodiment is formed by anode entrance zone 24 c and an expansion zone30 which is configured as a discontinuity in plasma passage 26.Downstream neutral insert 84 may have a circular lip 92 protruding intoexpansion zone 30 and having G2 vortex orifices 94 connected withcircular gas distributor 54 and forming Vort2 in the transition zone. G2plasma gas is fed into gas passage 52 located in anode housing 48 andconnected with circular gas distributor 54 formed by ceramic ringinsulator 28 and additional insulating ceramic ring 96. It may be notedthat the position of vortex orifices may be changed for the anodeentrance zone by just modification of ceramic rings 28 and 96.

FIGS. 14 a-b illustrate more features of an embodiment of downstreamneutral insert 84 having 6 vortex holes having diameter Dvor2. Theamount of holes and their diameters may be used to control the vortexintensity Vort2=G2/S2 and to adjust the vortex intensity to satisfy therequirements disclosed above. For example for six holes having diameterDvor2=0.6 mm surface area S2 is approximately 1.7 mm². Thus, inaccordance with a requirement 0.4 g/((sec)(mm²))>Vort2>0.1g/((sec)(mm²)) disclosed above, this vortex distributor may be used forgas flows G2 within 0.68 g/sec>G2>0.17 g/sec. Thus, nitrogen flow ratein this case may be estimated within 8.6-34.5 L/min. For other ranges ofG2 vortex gas flow amount and/or diameter of vortex holes may beadjusted accordingly. It may be noted that in this embodiment DG2 isabout 19 mm. Thus, it may be utilized for a significant range of DN forup to DN=16-17 mm providing a wide range of plasma velocity control

A plasma forming means (F) in this embodiment are not electricallyinsulated from the anode and may include the abrupt stepped expansion160 having diameter Ds. which may be located downstream of anode arcroot attachment 15.

The feedstock feeding module is not illustrated in FIG. 12 for claritypurposes. However, widely available powder injectors and powder injectorholders manufactured by various third parties may be adopted for thisembodiment.

Multiple trials have been performed for the method and apparatusdescribed herein. It was confirmed that the torch generates uniqueextremely stable plasmas having specific power within 43-140 kJ/g havingmore than 50 vol. % of molecular gases. However, it should be noted thatin the context of the present invention, the plasmas may have specificpowers of any one or more of the individual numerical value in thisrange, such as 43 kJ/g, 44 kJ/g, 45 kJ/g, 46 kJ/g, 47 kJ/g, etc., 48kJ/g, 49 kJ/g, 50 kJ/g, 51 kJ/g, 52 kJ/g, 53 kJ/g, 54 kJ/g, 55 kJ/g, 56kJ/g, 57 kJ/g, 58 kJ/g, 59 kJ/g, 60 kJ/g, 61 kJ/g, 62 kJ/g, 63 kJ/g, 64kJ/g, 65 kJ/g, 66 kJ/g, 67 kJ/g, 68 kJ/g, 69 kJ/g, 70 kJ/g, 71 kJ/g, 72kJ/g, 73 kJ/g, 74 kJ/g, 75 kJ/g, 76 kJ/g, 77 kJ/g, 78 kJ/g, 79 kJ/g, 80kJ/g, 81 kJ/g, 82 kJ/g, 83 kJ/g, 84 kJ/g, 85 kJ/g, 86 kJ/g, 87 kJ/g, 88kJ/g, 89 kJ/g, 90 kJ/g, 91 kJ/g, 92 kJ/g, 93 kJ/g, 94 kJ/g, 95 kJ/g, 96kJ/g, 97 kJ/g, 98 kJ/g, 99 kJ/g, 100 kJ/g, 101 kJ/g, 102 kJ/g, 103 kJ/g,104 kJ/g, 105 kJ/g, 106 kJ/g, 107 kJ/g, 108 kJ/g, 109 kJ/g, 110 kJ/g,111 kJ/g, 112 kJ/g 111 kJ/g, 112 kJ/g, 113 kJ/g, 114 kJ/g, 115 kJ/g, 116kJ/g, 117 kJ/g, 118 kJ/g, 119 kJ/g, 120 kJ/g, 121 kJ/g, 122 kJ/g 123kJ/g, 124 kJ/g, 125 kJ/g, 126 kJ/g, 127 kJ/g, 128 kJ/g, 129 kJ/g, 130kJ/g, 131 kJ/g, 132 kJ/g, 133 kJ/g, 134 kJ/g, 135 kJ/g, 136 kJ/g, 137kJ/g, 138 kJ/g, 139 kJ/g and 140 kJ/g. For example, one may havespecific powers of 50 kJ/g-140 kJ/g, or 60 kJ/g-140 kJ/g, or 70 kJ/g-140kJ/g, or 80 kJ/g-140 kJ/g or 90 kJ/g-140 kJ/g, 100 kJ/g-140 kJ/g, 110kJ/g-140 kJ/g, 120 kJ/g-140 kJ/g, and 130 kJ-140 kJ/g.

Accordingly, reference to a stable plasma herein may be understoodas: 1. No drifting or variations of average voltage above 1-2% of setupvalues during the life of the electrodes where the electrodes may have alifetime of 30 hours, 40 hours, 50 hours, etc., depending upon the levelof specific power; and (2) No high frequency (on kHz level) pulsing ofplasma voltage of more than ±10 V.

During the trials long term variations of average torch voltage weremainly observed on a level below 1%. Several observed variations on alevel of 1-2% may be attributed to unavoidable minor variations ofplasma gas flow due to ±1% accuracy of mass flow controllers used. Highfrequency pulsing of plasma voltage was on a negligible level below 5-10V which resulted in homogeneous treatment of feedstock, high depositefficiency and deposit quality. Durability trials showed long life ofelectrodes. For example, at SP of about 45-75 kJ/g life of electrodesmay be estimated on a level of 80-100 hours or above. At SP of about80-95 kJ/g life of electrodes may be estimated on a level above 40-50hours or above.

It may be also noted that the disclosed embodiment showed simultaneouscapability of generating relatively low specific power stable plasmashaving SP<43 kJ/g.

The method and apparatus described herein may used to apply coatings ona variety of substrates. These may include, e.g. power generatingcomponents which may be understood as any component used in a device forthe generation of powder. This may therefore include blades, vanes,combustors, liners, etc. One may also utilize the method and apparatusherein for coating of chambers which are used for application of vapordeposition materials.

Table 1 contents examples of parameters used to deposit differentcoatings based on the disclosed method and apparatus herein. Highdeposit efficiency as well as superior quality of coatings was observed.Some of the significant observations were as follows.

Example 1 is related to Cr₂O₃ coatings sprayed by a powder manufacturedby HC Starck and demonstrated high microhardness of about HV 1400-1500.

Example 2 is related to NiCrAlY coatings which demonstrated extremelylow oxides content and permeability and, therefore, high corrosionresistance. It may be noted that application of a deflection jet in thiscase resulted in the further decreasing of oxides content andpermeability. The deflection nozzle was 40 mm wide with a height ofabout 2.5 mm and was located 80 mm downstream of a powder injector.Compressed nitrogen at pressure of about 4 bars was used for thedeflection jet. Spray distance was 110 mm.

Examples 3-5 are related to thermal barrier porous coatings sprayed byspray-dry and sintered ZrO2-8% Y2O3 powder (ZRO-182 manufactured byPraxair). All coatings demonstrated pronounced porosity with averagepores size of about 4-8 microns. Total porosity of the coatings was asfollows: coating #3—28-30%; coating #4—33-35%; Coating #5—16-18%.

Examples 6-7 are related to thermal barrier dense coatings havingvertical cracks and sprayed by fused and crashed powder PC-YZ8tmanufactured by St. Gobain. It may be noted that coating #7 demonstratedhigher density of vertical cracks due to higher specific powers.

It may be noted that plasma coatings are, as a rule, sprayed by multiplepasses of plasma torch relatively spraying surface. Therefore, a coatingmay consist of multiple layers and each of them may be sprayed atdifferent conditions and/or by different feedstock thus satisfyingspecific requirements to the coating structure, composition andperformance. For example, thermal barrier coating (TBC) may consist of ametallic bond coat (BC) and ceramic top coat (TC) and each of them mayhave multiple layers sprayed by multiple plasma torch passes. Each layermay generally have a thickness of about 10-50 microns. Thus, totalcoating having thickness, for example, 500 microns may be sprayed by10-50 passes and has, consequently 10-50 layers. It may be noted thathigh SP molecular plasmas may be needed only to spray some layers. Forexample, SP>43 kJ/g may be needed only to spray first layer or layers ofa BC providing a good bonding and interface with a substrate. Anotherexample may be TC coating having a pronounced porosity and sprayed bybig ceramic particles having average size 60-100 microns which may alsoneed SP>43 kJ/g. It may be noted that some layers may be sprayed bydifferent methods. For example, some BC layers may be sprayed by LowPressure Plasma Spraying (LPPS) or by High Velocity Oxygen Fuel (HVOF)processes. Thus, the disclosed method may be applied to just selectedlayers of a total coating.

What is claimed is:
 1. A plasma torch for depositing a coating at avoltage (U) above 100 V and current (I) below 500 A comprising: acathode electrode, an anode module having an anode electrode having ananode axis, entrance zone and a cylindrical portion having diameter Dawherein said plasma torch generates a plasma arc having an anode arcroot attachment inside said anode; a plasma jet forming module locateddownstream of said anode arc root attachment which forming modulecontrols one or more parameters of the plasma jet in said module; aninterelectrode module controlling said plasma arc passage between saidcathode and said anode having one end adjacent said cathode module and asecond end adjacent said anode module and having a pilot insert adjacentto said cathode; at least one neutral inter-electrode insert; saidplasma torch further comprising two passageways to feed plasma gas in atotal amount G wherein said plasma gas comprises more than 50 vol. % ofmolecular gas; wherein (U)(I)/(G) is in the range of 43 kJ/g-140 kJ/g;wherein one of said passageways for feeding plasma gas comprises a firstplasma gas passage located between said cathode and pilot insert forfeeding plasma gas in amount G1 wherein said gas is directed through aplurality of orifices having a surface area S1 wherein a vortex isformed having a vortex intensity Vort1=G1/S1; wherein one of saidpassageways for feeding plasma gas comprises a second plasma gas passagelocated between said interelectrode module and said cylindrical part ofanode for feeding plasma gas in an amount G2; wherein said gas isdirected through a plurality of orifices having a surface area S2wherein a vortex is formed having a vortex intensity Vort2=G2/S2; andwherein G1 is greater than 0.6G and Vort1=G1/S1 is greater than 0.1g/((sec)(mm²)) and wherein said Vort2 is greater than 0.1 g/((sec)(mm²))and smaller than 0.4 g/((sec)(mm²)).
 2. The apparatus of claim 1 whereinsaid plurality of orifices having a surface area S2 locate on diameterat least 2 mm greater than said Da.
 3. The apparatus of claim 1 whereinlength of said anode entrance zone is (0.5-1.5) of said Da.
 4. Theapparatus of claim 1 wherein said inter-electrode module has a pluralityof said neutral inter-electrode inserts, each having a diameter, whichdefines said plasma arc passage.
 5. The apparatus of claim 4 whereinsaid plurality of neutral inter-electrode inserts provides a plasma arcpassage of increasing diameter.
 6. The apparatus of claim 4 wherein saidplurality of neutral inter-electrode inserts defines a plasma arcpassage of constant diameter.
 7. The apparatus of claim 1 including aneutral inter-electrode insert positioned adjacent said anode whereinsuch insert has a diameter value of (0.8-1.25)Da.
 8. The apparatus ofclaim 1 wherein said forming module has a forming nozzle providing astepped expansion of the plasma jet passage from sad diameter Da todiameter Ds and wherein (Ds-Da)/2 is within (0.2-0.6)Da, wherein(0.2-0.6)Da=δ, wherein δ is the expansion ratio.
 9. The apparatus ofclaim 8 wherein said stepped expansion is defined by said expansionratio δ and an expansion angle α and α has a value of 8° to 25°.
 10. Theapparatus of claim 9 wherein a has a value of 10° to 18°.
 11. Theapparatus of claim 8 wherein said stepped expansion is positioned within45° to 80° of said anode axis.
 12. The apparatus of claim 1 wherein saidfeedstock module is configured to feed feedstock in the form of powder.13. The apparatus of claim 1 wherein said feedstock module is configuredto feed feedstock that at least partially contains a liquid.
 14. Theapparatus of claim 1 wherein a compressed gas deflection jet is appliedacross said plasma jet containing said feedstock.
 15. The apparatus ofclaim 1 wherein said molecular gas is nitrogen.